A tdr (without a scope for a visible display) needs to see a step
function, an impedance lump. A gentle variance will not be reported
well. Comparing a known good length of the same material to your
material using a sensitive impedance bridge should tell you if the
center conductor has migrated as that will change the impedance.
Velocity factor will be different too.
And now stand by for the folks who know.
Patrick NJ5G
On 4/12/2016 1:33 PM, David Aslin G3WGN wrote:
Hi all,
Looking for the TT brains trust to help me out with this issue:
I have two drums of LDF4-50 and one of LDF5-50 which have been stored on their
sides for around 10 years. This disobeys one of the prime directives, since
Andrew/Commscope say they MUST be stored with the drums vertical. My
understanding is that the horizontal storage may lead to inner conductor
migration.
QUESTIONS: How can I determine whether migration has occurred; if so to what
extent; and what extent should cause me to avoid using the cable for the
50m/165ft+ runs to my HF towers?
Of course, if there is gross migration, a continuity check from inner to outer
would reveal a short, but would a TDR or other method reveal performance
degradation from lesser amounts of migration?
73, David G3WGN M6O
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